Technical Abstract:
Texture is central to consumer acceptability of peanut butter and peanut-based food products in general. The majority of peanuts are roasted; however, the effect of this operation on peanut texture was unclear. Accordingly, runner peanut seed (Arachis hypogaea L.) were dry roasted in a forced air convection oven at 164°C from 0 to 77 min. Upon removal from the oven, peanuts kernels were blanched (to remove testate) and seed color was determined using a Hunter Lab DP9000. Darker kernels were associated with increased roast time as reflected in lower L-value scores. Subsequently, 100g of roasted peanuts were ground to a paste, which is a precursor to peanut butter. Under constant grinding conditions, time until pasting decreased as roast intensity increased. A method was developed, using a TA.XT.plus Texture Analyzer, to measure peak force of peanut pastes upon compression with a 7mm diameter cylindrical flat bottom probe. Peak force of all roasted samples decreased until 35min, after which peak force increased as roast time increased. Soluble protein content at pH 8 in peanut pastes steadily decreased as the roast time increased. Electrophoretic patterns of soluble protein revealed a decreased concentration of conarachin (high molecular weight protein fraction) and an increased concentration of low molecular weight polypeptides as roasting time increased. Viscosity and density measurements were determined in expressed peanut oils from roasted samples, but changes in these physical parameters were minimal. Fatty acid profiles (FAP) of expressed peanut oils from roasted samples were determined by gas chromatography-mass spectrometer. Significant changes in FAP were observed with changes in roast intensity, however differences were minor. As a whole, these data provide insights into textural changes in peanut pastes with changes in roast intensity, and should be of value to the peanut processing industry.